Heretofore, a fuel cell system including a fuel cell for receiving a supplied reactant gas (a fuel gas and an oxidizing gas) to generate a power has been suggested and put to practical use. In general, such a fuel cell system is provided with a fuel supply passage through which the fuel gas supplied from a fuel supply source such as a hydrogen tank flows to the fuel cell, and the fuel supply passage is provided with a pressure regulation valve (a regulator) which decreases the pressure of the fuel gas to be supplied from the fuel supply source to a constant value.
At present, a technology has been suggested in which an on/off valve for changing the supply pressure of the fuel gas is provided in the fuel supply passage, to change the supply pressure of the fuel gas in accordance with the operation state of the system. Moreover, in recent years, a technology has also been suggested in which a pressure sensor is disposed on the upstream side of the on/off valve, to control the on/off valve based on a value detected by the pressure sensor (e.g., see Japanese Patent Application Laid-Open No. 2005-302563). When the technology disclosed in this Patent Document is employed, the breakdown of the on/off valve can be judged.